1. Field of the Invention
This invention relates to fibrously reinforced elongated articles, including hollow elongated pressure conduits such as piping with integrally cast couplings or sockets. This invention also relates to a method of making such articles by combining a thermosetting resin with a reinforcing cylindrical sock inserted in a cylindrical rotating mold, casting the pipe by centrifugal force, and then curing to produce a hard reinforced plastic pipe having the general shape of the mold.
2. Description of the Prior Art
Essentially two methods of constructing fiberglass reinforced pipe are known. The first method is known as a wrap method, wherein doped or impregnated fiberglass material is wrapped around the exterior surface of a mandrel which forms the inside diameter of the pipe. Successive layers of the doped fiberglass material are wrapped until the outside diameter of the pipe is achieved. The wrap method is labor intensive and therefore very expensive.
An alternate and more economical method of manufacturing fiberglass reinforced pipe is by centrifugally casting the pipe. This method and its product have been described in various documents, among them U.S. Pat. No. 3,093,160 to Herbert D. Boggs.
A typical apparatus for producing centrifugally cast fiberglass reinforced pipe has been described in U.S. Pat. No. 3,112,530 to Herbert D. Boggs. Suitable materials for use in the manufacture of the pipe have been described in U.S. Pat. Nos. 4,018,250 to William D. Waters and 4,097,569 to William D. Waters.
Centrifugally cast fiberglass reinforced pipe has generally consisted of a tubular product with a uniform inside diameter and a uniform outside diameter. To be manufactured in a commercially feasible manner the pipe is cast in standard lengths, typically 10, 20 and 30 foot lengths. However, to be used in a practical installation such as a chemical refinery or a waste water treatment facility the lengths of pipe must be joined together. The joining of the pipe has been accomplished by means of either molded couplings or handwrapped couplings. Each end of a coupling is glued or cemented to one end of a separate length of pipe. This end-to-end joining of lengths of pipe through couplings is labor intensive, expensive and time consuming.
Joining two lengths of centrifugally cast fiberglass reinforced pipe by means of a coupling can sometimes produce failure in the coupled pipe as there has been no practical way to guarantee that each length of pipe penetrates one-half the length of the coupling. Unless each length of pipe penetrates only half of the coupling, the integrity of the pipe and the coupling can not be relied upon. Thus premature and unwanted leaks of the piping system have been encountered.